Method for determining distances in the anterior ocular segment

Abstract

The invention relates to a method for determining distances in the anterior ocular segment, preferably of the pupils and/or the diameter of the iris, wherein the image of at least part of the eye is recorded and digitized using an imaging device and an array for illuminating the eye. On the basis of said digital image, a center of gravity analysis and the determination of the central point are carried out, especially for the position of the pupils, by conducting an intensity and threshold analysis as rough determination. Based on said rough determination, a fine detection of the position of the edges of the pupil and/or the edges of the iris is carried out. Additionally, the angle between the visual axis and the optical axis of the eye can be determined from the position of a fixed reflection to the center of the pupil and/or the center of the iris.

1. A method for measuring a pupil diameter and/or an iris diameter, comprising of:
 capturing an image of at least part of the eye with an image capture unit and an illumination system; 
 digitizing the captured image; 
 determining rough values of a pupil center and a radius of the pupil via an intensity threshold analysis; and 
 performing a fine detection of edges of the pupil and/or an iris on the basis of the rough determination 
 
     wherein the fine detection comprises
 scanning the digitized captured image along linear paths generally crossing the roughly detected pupil center wherein edges are detected along the linear paths and wherein the linear paths are within a limited angular region around a horizontal axis of the pupil; and 
 modeling the iris and the pupil by using a generally circular or a generally elliptic model of the edges of the iris and the pupil. 
 
   
   
     2. The method as claimed in  claim 1 , in which the structure whose edges are finely detected is selected from a group consisting of the pupil and the iris. 
   
   
     3. The method as claimed in  claim 1 , further comprising the step of determining an intersection point of a visual axis of the eye with a cornea by the use of a fixation light. 
   
   
     4. The method as claimed in  claim 1 , further comprising the step of determining an intersection point of a visual axis with the cornea with relation to the pupil or the iris on the basis of a position of a fixation reflection. 
   
   
     5. The method as claimed in  claim 1 , further comprising the step of determining an angle between a visual axis of the eye and an optical axis of the eye based on a position of a fixation reflection relative to a center of the pupil or a center of the iris. 
   
   
     6. The method as claimed in  claim 5 , further comprising the step of preadjusting an instrument for interferometric measurement of the segments of the eye along the optical axis of the eye using the angle determined. 
   
   
     7. A device for measuring a pupil diameter and/or an iris diameter, comprising:
 an image capture unit to capture an image of at least a portion of the eye; 
 an illumination system to illuminate the eye to facilitate the image capture; 
 a digitizer to digitize the captured image; 
 a microprocessor; and 
 software adapted to direct the microprocessor to determine rough values of a pupil center and a radius of the pupil; and subsequently, a fine detection analysis to determine the position of the edges of the structure based on the rough location 
 
     wherein the fine detection comprises:
 scanning the digitized captured image alone linear paths generally crossing the roughly detected pupil center wherein edges are detected along the linear paths and wherein the linear paths are within a limited angular region around a horizontal axis of the pupil; and 
 
     modeling the iris and the pupil by using a generally circular or a generally elliptic model of the edges of the iris and the pupil. 
   
   
     8. The device as claimed in  claim 7 , in which the structure of whose edges are finely detected is selected from a group consisting of the pupil and the iris. 
   
   
     9. The device as claimed in  claim 7 , further comprising software to direct the microprocessor to determine an intersection point of a visual axis with the cornea by the use of a fixation light. 
   
   
     10. The device as claimed in  claim 7 , further comprising software to direct the microprocessor to determine an intersection point of a visual axis with the cornea with relation to the pupil or the iris on the basis of a position of a fixation reflection. 
   
   
     11. The device as claimed in  claim 7 , further comprising software to direct the microprocessor to determine an angle between a visual axis of the eye and an optical axis of the eye based on a position of a fixation reflection relative to a center of the pupil or a center of the iris. 
   
   
     12. The device as claimed in  claim 11 , further comprising software to direct the microprocessor to preadjust an instrument for interferometric measurement of the segments of the eye along the optical axis of the eye using the angle determined. 
   
   
     13. A device for measuring a pupil diameter and/or an iris diameter, comprising:
 means for capturing an image of at least part of the eye; 
 means for illuminating the eye; 
 means for digitizing the captured image; 
 means for performing rough values of a pupil center and a radius of the pupil via an intensity threshold analysis; and 
 means for performing a fine detection of edges of the structure on the basis of the rough determination 
 
     wherein the fine detection comprises:
 scanning the digitized captured image along linear paths generally crossing the roughly detected pupil center wherein edges are detected along the linear paths and wherein the linear paths are within a limited angular region around a horizontal axis of the pupil; and 
 modeling the iris and the pupil by using generally circular or a generally elliptic model of the edges of the iris and the pupil. 
 
   
   
     14. The device as claimed in  claim 13 , in which the structure whose edges are finely detected is selected from a group consisting of the pupil and the iris. 
   
   
     15. The device as claimed in  claim 13 , further comprising means for determining an intersection point of a visual axis with the cornea by the use of a fixation light. 
   
   
     16. The device as claimed in  claim 13 , further comprising means for determining an intersection point of a visual axis with the cornea with relation to the pupil or the iris on the basis of a position of a fixation reflection. 
   
   
     17. The device as claimed in  claim 13 , further comprising means for determining an angle between a visual axis of the eye and an optical axis of the eye based on a position of a fixation reflection relative to a center of the pupil or a center of the iris. 
   
   
     18. The device as claimed in  claim 17 , further comprising means for preadjusting an instrument for interferometric measurement of the segments of the eye along the optical axis of the eye using the angle determined.